N fare code

Bit of a rookie question I'm afraid, but my friend has booked in N (economy) and now wants to know if they can upgrade it to a flexible ticket so they can change dates.

So, can someone please tell me
a). If changing is possible
b). and how much that will cost

Thanks:D

VS.

If the N fare is a published fare (ie: airline direct fare) , they can most probably upgrade it for the difference in fare plus a change fee. If it a NETT ticket (ie: travel agent special offer or combined with Car Hire or hitel...) then they cannot be upgraded.

(edited to clarify response)